import java.util.Arrays;

public class PriorityQueue {
    public int[] elem;
    public int usedSize;

    public PriorityQueue() {
        elem = new int[10];
    }

    /**
     * 建堆的时间复杂度：O(N)
     *
     * @param array
     */
    public void createHeap(int[] array) {
        elem = Arrays.copyOf(array, array.length);
        usedSize = array.length;
        int child = array.length;
        for (int i = (child - 1) / 2; i >= 0; i--) {
            shiftDown(i, array.length);
        }
    }

    /**
     *
     * @param root 是每棵子树的根节点的下标
     * @param len  是每棵子树调整结束的结束条件
     * 向下调整的时间复杂度：O(logn)
     */
    private void shiftDown(int root,int len) {
        int child = root * 2 + 1;

        while(child < len) {
            if(child + 1 < len && elem[child] < elem[child + 1]) {
                // 有右树并且右树的元素比左边大
                child++;
            }
            // 此时 child 一定是较大着的下标
            if (elem[child] > elem[root]) {
                swap(child, root);
                root = child;
                child = root * 2 + 1;
            } else {
                break;
            }
        }
    }

    private void swap(int i, int j) {
        int t = elem[i];
        elem[i] = elem[j];
        elem[j] = t;
    }


    /**
     * 入队：仍然要保持是大根堆
     * @param val
     */
    public void push(int val) {
        if(isFull()) {
            elem = Arrays.copyOf(elem, elem.length + (elem.length >>> 1));
        }
        elem[usedSize] = val;
        shiftUp(usedSize);
        usedSize++;
    }

    private void shiftUp(int child) {
        int root = (child - 1) / 2;
        while(child > 0) {
            if(elem[child] > elem[root]) {
                swap(child, root);
                child = root;
                root = (child - 1) / 2;
            } else {
                break;
            }
        }
    }

    public boolean isFull() {
        return usedSize == elem.length;
    }

    /**
     * 出队【删除】：每次删除的都是优先级高的元素
     * 仍然要保持是 大根堆
     */
    public void pollHeap() {
        if(isEmpty()) {
            return;
        }
        swap(0, usedSize - 1);
        usedSize--;
        shiftDown(0, usedSize);
    }

    public boolean isEmpty() {
        return usedSize == 0;
    }

    /**
     * 获取堆顶元素
     * @return
     */
    public int peekHeap() {
        return elem[0];
    }
}